Hydrogen concentration, discrepancy between

Both predictions are related to the experimental concentration profiles measured in our previous studies [13]. The results obtained with the HM are very close to these obtained with the conventional approach (CM) - see solid and dotted lines in Figs. 4a-b. Only small differences in the distribution of the intermediate compounds B and C are noticed the maxima on the concentration vs. curves for these compounds are located at almost the same values of the hydrogen conversions Ch- For both, conventional and neural network approaches, some discrepancies between predicted and experimental concentration profiles can be observed for compounds A and B at Tr = 345 K. We observe also a short-coming of the neural network approach. At full hydrogenation of the original reactant, that is at Ch = 1 00, a still not completed conversion is predicted. Further we may observe that in Fig. 4b at = COO still B and D are... 

We shall now consider how far the rates of simple proton-transfer reactions fulfil these predictions. It should first be noted that velocity constants of the magnitude with which we are concerned are not known with any accuracy, and that the discrepancies between the results obtained by different methods are frequently far outside the limits of error estimated by the investigators. This is illustrated by Table 16 which collects rate constants reported for the reaction between hydrogen ions and acetate ions in aqueous solution. Although some of the discrepancies may be due to differences in experimental conditions (e.g., electrochemical methods often involve the use of high concentrations of inert electrolyte ), there are certainly considerable differences which must stem from experimental or theoretical uncertainties in the techniques used. Caution is therefore necessary in interpreting minor variations in velocity constants of this magnitude, especially if they have been obtained by different methods. 

If the buffered solution is dilute, this is its hydrogen-ion concentration. Because the activities of ions are affected by other ions, however, there is appreciable deviation from the calculated values in salt solutions as concentrated as 0.1 M. This fact accounts for the small discrepancies between the pH values calculated from equilibrium constants and those given in the buffer tables. 

A fifth paper on this reaction seeks to clear up discrepancies between two sets of activation parameters reported for the k and k terms of this rate law. This paper also briefly discusses reactivities of 0x0- and hydroxo-bridged transition-metal complexes. Reactivities of these compounds can be compared with those for similar actinide species through kinetic results for decomposition of, for example, the [U020H]a + dimer, and the peroxo-bridged plutonium species [Pu—O2—PuOH] +. The rate of decomposition of this last complex is proportional to hydrogen ion concentration— there is just one acid-catalysed path here, in contrast to the parallel pH-dependent and pH-independent paths for the [Fe(OH)]a + dimer. 

Despite its obvious importance, the interpretation and even the measured yields in the radiolysis of water vapor were doubtful until the sixties. It was not because of lack of experimental data rather, it was because of difficulties of comparing measurements of different workers due to artifacts and sheer experimental problems (Anderson, 1968). The greatest discrepancy is in the reported hydrogen yields, which varied between the extremes by a factor of -104 (Dixon, 1970 Anderson, 1968). It is now agreed that G(H2) in water vapor at 1021 eV/g varies around 10-3. But, as pointed out by Dixon, the absolute yield of hydrogen in pure water vapor is not a very meaningful quantity, because a steady state is achieved and a consistent steady state concentration of H2 and 02 may be... 

The exact values for the rate constants for hydrogen abstraction by triplet benzophenone are not yet entirely certain. Three groups338-338 have reported a value of 108M-1 sec-1 for abstraction from 2-propanol in concentrated 2-propanol, while the combination of the data of three other groups333,338 339 for dilute benzene solutions yields a value of only 105M-1 sec-1. This discrepancy could well reflect a solvent effect such as that found in studies of the reactivity of alkoxy radicals.340 However, the hundredfold difference between the reported rates for attack of triplet benzophenone on toluene338,338 undoubtedly reflects experimental problems, because both values were measured in aromatic solvents. 

Much of the reported work on the hydration of olefins has tried to fit the acid-dependence of the reaction either to the stoichiometric hydrogen ion concentration or to the origin Hammett function. In the latter case, even when the reaction shows linear dependence upon //o, the slope of the plot is often greater than unity. It has been suggested that this discrepancy is due to changes in the activity coefficient terms similar to the variations found between the different acidity functions , viz-... 

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